For example, as described in Patent Literature 1, there has been known a solenoid for an electromagnetic valve, in which a stationary iron core is mounted in a center hole of a bobbin with an exciting coil wound therearound, a movable iron core is slidably inserted in the center hole, and a magnetic path is connected between a magnetic frame shaped like a cover surrounding the bobbin and an end of the stationary iron core opposite the movable iron core. A magnetic plate for forming a magnetic path between the magnetic frame and the movable iron core is provided around a side of the movable iron core opposite an attracting-force acting surface of the stationary iron core, and the movable iron core is attracted toward the stationary iron core by application of current to the exciting coil or is separated from the stationary iron core by biasing force of a return spring so as to open and close a valve member. A portion of the magnetic plate opposing an outer peripheral surface of the movable iron core extends toward the stationary iron core along a surface of the movable iron core.
In the above-described solenoid for the electromagnetic valve, a magnetic path is formed to reach from the stationary iron core to the movable iron core through the magnetic frame surrounding the bobbin and the magnetic plate and to return to the stationary iron core. A gap between the movable iron core and the stationary iron core and a space between the movable iron core and the magnetic plate are great magnetic resistances in the magnetic path. Even if a relatively great magnetic resistance is produced in other portions, it is relatively easy to reduce the magnetic resistance by a structure change.
Since the gap between the movable iron core and the stationary iron core corresponds to a stroke of the movable iron core during energization of the exciting coil, the magnetic resistance can be reduced by minimizing the stroke by a valve structure or the like, but the gap is basically essential. While the space between the movable iron core and the magnetic plate is also a great magnetic resistance, the space is necessary to cause the movable iron core to make a stroke without contact with the magnetic plate. However, magnetic efficiency of the solenoid for the electromagnetic valve can be enhanced by reducing the magnetic resistance in some way.